Due to the tremendous volume of mail processed daily in the United States and other countries, mail sorting equipment has become increasingly complex. Sophisticated scanning equipment along with computer controlled high speed conveying and sorting machines are used to process ever increasing volumes of postcards, letters, magazines, parcels and other types of mail. The dynamics of mail processing is the outcome of the interplay of various driving forces that must be controlled. The mail undergoes action of various forces from one point in a machine to another in a number of steps. Action of the forces determines the spatial configuration, such as the location, orientation, instantaneous velocity and acceleration of the mail.
Conveyor belts are one of the most important components in the drive system of current mail sorting machines. Mail is moved through these machines with contact between the belt surface and the mail surface being the primary source of propulsive force for the mail movement. Apart from the propulsive force, constraining forces must be applied to the mail pieces in order to maintain the desired distance between the mail pieces, avoid accumulation of mail within the machine and avoid damage to the mail due to shearing, tearing and bending of the mail. Optimally applied forces allow smooth propulsion of the belt. Action of any unbalanced force may change the dynamic configuration of the belt and mail and may eventually lead to improper functioning of the machine, damage of the mail pieces and/or damage to the machine.
The fundamental structural properties and the harsh dynamics of the process environment make the belts prone to wear and, in many cases, failure. On the other hand, mail processing facilities and equipment are necessarily designed having areas for which access must be restricted during processing. For example, letter and mail processing machines have interlocked doors and covers such that runtime access is prohibited for safety and security reasons. Many areas within mail handling machines and systems cannot be viewed during operation. Additionally, in large material handling systems, it is simply not practical to provide operator access to all areas of the system. Determining the condition of belts used in mail sorting and handling machines can therefore be an involved, cumbersome and eventually expensive process.
The current method of determining whether a conveyor belt needs to be replaced or repaired involves visual and manual inspection by maintenance personnel. The maintenance personnel touch the belt to examine it for surface wear and look for visual indications of fraying and cracking. In addition they examine the belt during operation for improper tracking, scalloping, improper tension, bad alignment etc. Since mail sorting machines may have several hundred conveyor belts, many of which are hidden behind panels or in hard to access areas, the task of inspecting the belts is time consuming and sometimes ineffective. Further, some modes of belt failure have no advance visual indications. As a result, conveyor belts fail during operation reducing the reliability of the machine.
A fundamental issue in high volume processing operations is the conflict between the desire to operate a machine and the need to halt the machine to perform needed belt replacement, maintenance and troubleshooting functions. Generally, maintenance managers must negotiate time with production or operations management for down-time in which to perform needed repairs. There is an element of risk that if a machine is taken down for troubleshooting and repair, it may not be available for the next processing cycle. In many cases, troubleshooting the problem requires more time than the actual repair, once the problem is known. At various sites requiring a high through-put there is a trend to replace belts whether needed or not needed in order to prevent costly downtime.
Timely diagnostics of belt parameters suggest the state of belt. With the state of belt known, the preventive action and the schedule for maintenance can be determined. Also the cost associated with the replacement of belts due to uncertainties can be eliminated.